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![Page 1: DTSC VAPOR INTRUSION GUIDANCE California Industrial Hygiene Council 16 th Annual Conference Dan Gallagher Department of Toxic Substances Control California.](https://reader035.fdocuments.us/reader035/viewer/2022062516/56649e445503460f94b38c14/html5/thumbnails/1.jpg)
DTSC VAPOR INTRUSION GUIDANCE
California Industrial Hygiene Council16th Annual Conference
Dan GallagherDepartment of Toxic Substances Control
California Environmental Protection Agency
December 5, 2006
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Vapor Intrusion – Conceptual Model
VOC SOURCE
Diffusion
DiffusionAnd
Advection
Stack Effects(heating and air
conditioning)
cracks
Barometric PressureWind
Temperature
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Vapor Intrusion Guidance Document
Step 1: Identification of a Spill or Release– Knowledge of site history, and past and
present industrial practices
Step 2: Site Characterization– Site inspection (receptors and buildings)– Three dimensional definition of
contamination
Guidance is Presented as a Series of Steps
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Plume Characterization
Hierarchy of Sampling for the Evaluation of Vapor Intrusion
1. Soil Gas
2. Groundwater
3. Soil Matrix (Method 5035)
4. Flux Chambers
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Screening Sites with Groundwater
Groundwater monitoring wells must be screened properly
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Flux Chambers
Taken From LUSTLine Bulletin 44
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Flux Chambers
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Vapor Intrusion Guidance Document
Step 3: Is the Site a Candidate for Vapor Intrusion?
- Volatile organic compounds (VOCs) at the site (list provided in the guidance)?
- Are buildings located near the VOCs (100 lateral feet)?
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Vapor Intrusion Guidance Document
Step 4: If Pathway is Complete, Evaluate Imminent Hazard
– Receptor symptoms
– Odors
– Wet basements
– Evaluate for fire and explosive conditions
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Vapor Intrusion Guidance Document
Step 5: Conduct Preliminary Screening for the Building
– Senate Bill 32 required the Office of Environmental Health Hazard Assessment (OEHHA) to develop screening numbers for vapor intrusion
– OEHHA screening numbers can be used to “estimate the degree of effort” for site cleanup but the numbers are risk-based
– Cal-EPA published a user’s guide for the screening numbers (www.calepa.ca.gov)
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OEHHA generated soil screening levels in 2005 for seventeen volatile chemicals pursuant to SB 32
ChemicalProtective Soil Gas
Concentration (Residential)
Benzene 0.04 ug/L
Trichloroethylene (TCE) 0.5 ug/L
Tetrachloroethylene (PCE) 0.2 ug/L
Vinyl Chloride 0.01 ug/L
EXAMPLE OF SOIL GAS CHHSLs
California Human Health Screening Levels (CHHSLs)
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Vapor Intrusion Guidance Document
Step 6: Collect Additional Field Data
– Collect air samples from crawl spaces
– Collect soil gas samples directly under the building foundation (subslab)
– Measure the physical properties of the soil, such as:
• porosity• air permeability• moisture content• bulk density
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Vapor Intrusion Guidance Document
Step 7: Conduct a Site-Specific Modeling Evaluation for the Building
– Use the Johnson and Ettinger Model (JEM)
– Use site-specific geotechnical and building input parameters for modeling
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Vapor Intrusion Guidance Document
Step 8 and 9: Building Pathway Evaluation and Indoor Air Sampling
– Building occupancy survey
– Identify sources of indoor contamination with field analytical equipment
– Sample indoor air twice over a year to evaluate human exposure using TO-14A / TO-15 [SIM]
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Indoor Air Sampling Results (minimum of 2
sampling events needed)Response Activities
Risk: <10-6
HQ: <1.0Minimal
Determine that the soil gas plume is
stable
Risk: 10-4 - 10-6
HQ: 1.0 – 3.0Monitoring
Install and sample subslab and/or
vadose zone monitoring probes
Risk: >10-4
HQ: >3.0Mitigation
Institute engineering controls and
continue indoor air sampling
Vapor Intrusion Guidance DocumentStep 10: Evaluation of Indoor Air Data
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Vapor Intrusion Guidance Document
Step 11: Mitigate Indoor Air Exposure
– Remediate the subsurface contamination
– Land use covenants to restrict property use
– Engineering controls to eliminate exposure
Long-term monitoring may be required
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Land Use Covenants (LUCs)
Title 22 CCR Section 67391.1
– LUC must be used when contamination exceeds residential standards
– LUC is executed by DTSC and owner and should run with the land
– Response action is not complete until LUC is signed and recorded at the county
– Owners, operators, and proponents pay all cost associated with administration, including DTSC time
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Land Use Covenants (LUCs)
Protect Public from Unsafe Exposure
– Identification of responsible party
– Restrict building locations
– Barriers and vent systems
– Soil management plan
– Monitoring and associated reporting
– DTSC inspections (cost reimbursement)
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CASE STUDY
Chemical Distribution Center in Los Angeles
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ionconcentrat gas soil
ionconcentrat air indoor )( factor nattenuatio
Definition of Attenuation Factor
For reference, the OEHHA attenuation factor for existing residential structures is 0.002
(CHHSLs)
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Chemical Distribution Center
100 FEET
UNDERGROUNDSTORAGE
TANKS
HAZARDOUS WASTE STORAGE AREAABOVEGROUND STORAGE TANKS
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TETRACHLOROETHYLENE (PCE) SOIL GAS CONCENTRATIONS: 5 FEET BELOW SURFACE
Shallow Soil Gas Plume
200 FEET
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PROTECTIVE SOIL GAS CONCENTATIONS
PCE Soil Gas Concentration at Nearest Residence = 48 ug/L
Residential CHHSL for Tetrachloroethylene (PCE) is 0.2 ug/L
PRELIMINARY SCREENING
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Nearest Residential Structure
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Median Conservative
Total Porosity 0.44 0.50
Water-Filled Porosity 0.30 0.19
Permeability (cm2) 5.8 x 10-9 1.9 x 10-8
Median Conservative
Attenuation Factor (Modeling) 0.00008 0.0005
PCE Cancer Risk 1 x 10-5 7 x 10-5
Predicted PCE Indoors (ug/L) 0.004 0.024
FATE AND TRANSPORT MODELING
13 Laboratory Geotechnical Measurements: 5 - 8 feet below grade
PCE Risk for nearest residence (PCE soil gas = 48 ug/L)
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ug/L
Residential CHHSL (PCE) 0.2
Site-Specific Screening Value (PCE) 0.8 – 5.0
PROTECTIVE SOIL GAS CONCENTATIONS
PCE soil gas concentration at nearest residence = 48 ug/L
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Homes Subject to Indoor Air Testing
September 2004
Conducted by USEPA
Declined
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Indoor and Outdoor Sampling Results (2004)
OEHHA Value for PCE in
Indoor Air = 0.0004 ug/L(risk = 10-6)
0.0001
0.001
0.01
0.1
PC
E C
on
ce
ntr
ati
on
(u
g/L
)
OUTDOOR INDOOR
3 Samples 8 Homesand 2 Apts
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Homes Subject to Vapor Intrusion
Indoor air in homes that tested positive for 1,1-DCE
Not Tested
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Response ActionDTSC Vapor Intrusion Guidance Document
Indoor Air Sampling Results (minimum of 2
sampling events needed)Response Activities
Risk: <10-6
HQ: <1.0Minimal
Determine that the soil gas plume is
stable
Risk: 10-4 - 10-6
HQ: 1.0 – 3.0Monitoring
Install and sample subslab and/or
vadose zone monitoring probes
Risk: >10-4
HQ: >3.0Mitigation
Institute engineering controls and
continue indoor air sampling
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SOIL VAPOR EXTRACTION WELLS
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Vapor Extraction Carbon Canisters
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0’
10’
40’
50’
85’
CONCEPTUAL CROSS SECTION
EXTRACTION WELLSOBSERVATION WELLS
ROI = +250 feet
ROI = 150 feet
NO VACUUM RESPONSE
CLAYCLAY
SILTY SAND
SAND
SILTY CLAY
WAREHOUSE
GROUNDWATER
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OFF-SITE VAPOR MONITORING WELLSVapor Extraction Started in May 2005
Offsite Concentration Response in the Silty Clay
0.01
0.1
1
10
100
3/1/2005 5/1/2005 7/1/2005 9/1/2005 11/1/2005
TIME
PC
E C
on
ce
ntr
ati
on
(u
g/L
)
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Indoor Air Sampling 11/05
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Outdoor Air Sampling 11/05
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Indoor and Outdoor Sampling Results (2005)
OEHHA Value for PCE in
Indoor Air = 0.0004 ug/L
(risk = 10-6)
0.0001
0.001
0.01
0.1
PC
E C
on
cen
trat
ion
(u
g/L
)
OUTDOOR INDOOR
7 Samples 8 Homesand 3 Apts